受限空间内细水雾与火相互作用的实验研究

细水雾灭火系统作为卤代烷系列灭火剂的替代产品之一，以其高效无毒、经济实用的优点，近年来在国际上研究得非常活跃。本文在受限空间内利用先进的材料热释放速率测量仪研究了细水雾与火的相互作用过程，并得到了以下结论：细水雾通过汽化吸热冷却燃料及氧化剂、体积膨胀隔氧以及吸收热辐射降低对燃料的热回馈等效应与火相互作用，达到控制和扑灭火灾的目的，在受限空间内汽化隔氧效应起着重要作用。     

Attenuation of a point blast shock wave in the dusty air

The behavior of the blast impulse initiated by a point blast in the dusty air is investigated theoretically. It is shown that the jumps of parameters at the shock front in the dusty air follow other regularities in comparison with the case of an ideal gas, beginning from the distance of three dynamic radii, so at ten dynamic radii the difference in overpressure exceeds 60%. When the air heterogeneity is taken into account, substantial gradual changes of wave profile come over and the total blast wave impulse can't be determined by the front overpressure only. The known far asymptotic law takes no place in the point blast flow at the volume dust densities ρ₂₀ > 3·10^?3 kg/m³. In contrast to the ideal gas, the shock front discontinuity vanishes in the dusty air at a finite distance from its origin and the blast wave eventually turns into a dispersive wave without discontinuity. The wave structure changing is studied in the process of the shock wave transformation into the dispersive wave.     

中国西南典型山地城市环境宜居性评价 ——以重庆市两江新区城区为例

城市环境宜居性评价对推动城市品质提升、功能优化有十分重要的意义.通过分析山地城市自然环境和人文环境的复杂特性,构建了涉及自然环境、人文便利性、人文舒适性、人文健康性、人文安全性5方面10个指标的城市环境宜居性评价体系.在此基础上,以重庆市两江新区城区为研究对象,通过评价指标计算、分级、赋权等工作,对城市环境宜居性进行了...     

反应堆压力容器保温层辐射屏蔽组件传热计算分析及屏蔽材料试验研究

目的 确保华龙一号HPR1000反应堆压力容器保温层辐射屏蔽组件在运行工况下的可靠性、安全性以及能够有效执行其功能。方法 采用基于传热理论结合经验公式的理论计算方法,以及流固耦合的有限元仿真分析,对辐射屏蔽组件的运行温度进行计算。针对屏蔽材料在受热状态下的性质变化,进行一系列的热态性质试验。结果 理论计算方法得到的结果为163.36~168.74 ℃,有限元仿真分析得到的结果为236.85~266.85 ℃,两者偏差约100 ℃。对造成该种差异的原因进行了分析,发现仿真分析方法得到的结果的置信度更高。屏蔽材料在受热状态下,其体积膨胀率可达到38.82%,而当屏蔽材料受热超过其温度限值204 ℃后,将出现明显的粉化等物理状态恶化的趋势。结论 流固耦合的有限元仿真分析方法更适用于辐射屏蔽组件的传热过程计算,同时获取了屏蔽材料物理性状受热变化趋势,对屏蔽组件的选材及结构设计具有指导意义。     

舰载机机载设备弹射和拦阻冲击试验条件研究

弹射和拦阻冲击试验是舰载机机载设备必要的考核试验之一,而目前相关标准并未明确试验具体量值,且国内缺少试验经验,这会影响试验工作的开展。基于此,从GJB 150.18A—2009规定的阻尼正弦波出发,结合项目研制过程数据,提出波形频率和振幅的确定方法。波形频率可根据类似机型的地面共振试验数据或全机振动模态分析结果确定,这里利用弹性缩比模型地面动响应试验和带通滤波法来预计瞬态波振幅,并说明了阻尼正弦波实施案例和对试验设备冲程的要求。从累积损伤角度出发,认为采用随机振动试验替代弹射和拦阻冲击试验是可行的,而不能采用常规冲击试验进行替代。根据随机振动3σ响应谱和冲击响应谱的对比分析,提出了采用振动功能试验替代弹射和拦阻冲击试验的前提条件——设备安装频率应高于要求值。     

矿井高温高湿职业危害及其临界预防点确定

为预防矿井高温高湿热害对矿工身心健康造成不良影响,对矿井热源以及高温高湿环境导致的职业危害进行分析。选取等效温度(TET)和综合温度指标(TZ)作为热应力指标,调查研究矿井高温高湿环境造成的矿工疲劳问题和烦恼问题。提出在矿井特殊环境下导致矿工疲劳和烦恼的临界预防点—TET指标临界值和TZ指标临界值分别为28.48℃和26.14℃,并给出矿井临界深度745 m。结果表明:提出的临界预防值与国内外已经制定的标准有一定的一致性。矿井开采超过临界深度后,矿工疲劳、烦恼影响程度将随开采深度急剧增加。不同深度矿井应该采取不同的降温标准。     

Ecological consequences of forest elephant declines for Afrotropical forests

Poaching is rapidly extirpating African forest elephants (Loxodonta cyclotis) from most of their historical range, leaving vast areas of elephant‐free tropical forest. Elephants are ecological engineers that create and maintain forest habitat; thus, their loss will have large consequences for the composition and structure of Afrotropical forests. Through a comprehensive literature review, we evaluated the roles of forest elephants in seed dispersal, nutrient recycling, and herbivory and physical damage to predict the cascading ecological effects of their population declines. Loss of seed dispersal by elephants will favor tree species dispersed abiotically and by smaller dispersal agents, and tree species composition will depend on the downstream effects of changes in elephant nutrient cycling and browsing. Loss of trampling and herbivory of seedlings and saplings will result in high tree density with release from browsing pressures. Diminished seed dispersal by elephants and high stem density are likely to reduce the recruitment of large trees and thus increase homogeneity of forest structure and decrease carbon stocks. The loss of ecological services by forest elephants likely means Central African forests will be more like Neotropical forests, from which megafauna were extirpated thousands of years ago. Without intervention, as much as 96% of Central African forests will have modified species composition and structure as elephants are compressed into remaining protected areas. Stopping elephant poaching is an urgent first step to mitigating these effects, but long‐term conservation will require land‐use planning that incorporates elephant habitat into forested landscapes that are being rapidly transformed by industrial agriculture and logging.     

Development and application of a new power analysis system for testing of geothermal thermoelectric generators

This article presents a new thermoelectric generator power analysis system (TEG-PAS) for the examination of all parameters of the thermoelectric generators (TEGs) operated by geothermal or any liquid heat. As a sample application, the developed TEG-PAS has been tried on a TEG of 100 W. During electrical energy generation, the values of the electrical, the thermo-electrical and the thermal variables of the TEG have been transmitted to the TEG-PAS by the employed sensors. Thus, the using of several devices simultaneously has been eliminated while the power performance analyses are being carried out.     

Performance improvement of a double-pass V-corrugated solar air heater under recycling operation

The device performance of double-pass V-corrugated solar air heaters with external recycle was investigated experimentally and theoretically. The comparison between V-corrugated and flat-plate collectors was made to show the thermal efficiency improvement with various operating parameters. The results show that the collector efficiency improvement of the recycling double-pass V-corrugated operation is much higher than those of the other configurations under various recycle ratios and mass flow rates. However, there exists the penalty on the power consumption increment due to implementing V-corrugated channel into the solar air heaters, an economic consideration on both the heat-transfer efficiency enhancement and power consumption increment for the double-pass V-corrugated device was also delineated. The experimental setup was carried out to validate the theoretical predictions, and the fairly good agreement between both results was achieved with the error analysis of 0.48-1.83%.     

Combustion features under different center of heat release of a diesel engine using dimethyl carbonate/diesel blend

Experiments were performed in a single cylinder common-rail diesel engine that adopts a low temperature premixed charge compression ignition (PCCI) mode. Combustion features of dimethyl carbonate (DMC)-diesel blends under various centers of heat release (COHRs) were revealed in details. With retarding of COHR, all the peaks of pressure and pressure rise rate and bulk gas temperature are postponed and declined in sequence. Normally, the crank angle of peak pressure is quite close to the COHR, while the peak of bulk gas temperature appears about 7°CA after COHR as a rule. The prolongation can be demonstrated at every stage of combustion such as q₁₀ and q₉₀ with the COHR being put backward. In addition, the heat release of diesel is completely slower than that of D10 fuel at various stages. Unfortunately, retarding of COHR implies a declining thermal efficiency of engines as well as a higher cyclic variation in general. Nevertheless, D10 blend has higher thermal efficiency than diesel thanks to high oxygen content of DMC and low boiling point that prompts better fuel atomization and complete combustion. Meanwhile, the cyclical variation of D10 is greater than diesel fuel owing to the low heat value, high latent heat of vaporization, and poor flammability of DMC. As a total, a comprehensive understanding of PCCI combustion features under different COHRs can be conducive to conducting effective management of combustion process and manipulating the subsequent emission performance to a favorable level.